1. Field of the Invention
The present invention relates to a solvent delivery pump for sending a solution by sliding a plunger in a pump head to repeatedly suck the solution from a sucking port and discharge the solution from a discharge port.
2. Description of the Related Art
A schematic sectional view of a vicinity of a pump chamber of an ordinary plunger-type solvent delivery pump is shown in FIG. 3A.
The solvent delivery pump sends a solution with the tip end portion of a plunger 3 sliding in a pump chamber 8a in a pump head 8 to repeatedly suck the solution from a sucking port 8b and to discharge the solution from a discharge port 8c. At a portion of the pump chamber 8a through which a plunger 3 is inserted, a resin plunger seal 13 in close contact with an outer periphery of the plunger 3 for preventing leakage of the solution from a clearance between an inner wall of the pump chamber 8a and the outer periphery of the plunger 3 is provided. The pump head 8 is retained on a pump body 18. The plunger seal 13 is sandwiched between the pump head 8 and the pump body 18.
The pump body 18 supports a back face of the plunger seal 13 on its wall face on a side of the pump head 8. This wall face is provided with a hole 20 through which the plunger 3 is to be passed. If a clearance between the hole 20 and the plunger 3 is large, cold flow occurs and an inner peripheral portion of the plunger seal 13 may enter the clearance between the hole 20 and the plunger 3 in some cases as shown in FIG. 3B when solution sending pressure becomes high (e.g., about 40 MPa). In this state, friction between the plunger 3 and the plunger seal 13 increases, which affects driving of the plunger 3 and shortens sealing life of the plunger seal 13.
Because of this, it is necessary to control a dimensional tolerance of an inner diameter of the hole 20 to reduce the clearance from an outside shape of the plunger 3. However, the pump body 18 is made of metal such as stainless steel and the plunger 3 which comes in contact with an inner peripheral face of the hole 20 seizes up, which sets a limitation on reduction of the inner diameter of the hole 20.
Therefore, if the solution sending pressure is high pressure over 70 MPa, for example, a backup ring 22 is disposed on a back face of a plunger seal 13 as shown in FIG. 4A (see Japanese Patent Application Laid-Open No. 2001-254686, for example). Material of the backup ring 22 is a resin material such as PEEK (polyether ether ketone) resin which is harder than material of the plunger seal 13 and does not affect the plunger 3 when the backup ring 22 comes in contact with the outer periphery of the plunger 3.
However, if the backup ring 22 made of the PEEK resin is used under a condition of higher sending pressure over 100 MPa, the plunger seal 13 is deformed under the high pressure to press against the backup ring 22, the backup ring 22 is deformed inward in a radial direction, and an inside diameter of the backup ring 22 reduces to increase contact resistance with the plunger 3, which affects driving of the plunger 3.
On the other hand, if material having a higher elastic modulus than the PEEK resin is used for the backup ring 22 as a resin which can bear deformation of the plunger seal 13 in order to prevent deformation of the backup ring 22, the backup ring 22 is not deformed at all, and therefore, the plunger seal 13 is deformed inward in the radial direction to apply a greater tightening force on the plunger 3, which affects driving of the plunger 3 and shortens the sealing life of the plunger seal 13.